Teens who ate three or more weekly servings had a 39 percent increased chance of developing severe asthma, while younger children had a 27 percent higher risk, according to a study of 319,000 teens in 51 countries and 181,000 children ages 6 and 7 in 31 countries. The research, led by scientists at the University of Auckland in New Zealand, was published today in the British medical journal Thorax.

The study didn’t prove that eating more fast food caused the increase in the conditions, which both can be linked to the overreaction of the body’s immune system. Because fast food was the only dietary category shown to have an association with the disorders, the results suggest that such a diet may cause asthma attacks or eczema outbreaks, the authors said. Conversely, eating three or more servings of fruit a week showed reduced risk in developing those conditions, they said.

"What’s clear from this study as that fruits and vegetables turned up as protective factors and fast foods turned up as risk factors," Gabriele Nagel, a senior researcher at the Institute of Epidemiology and Medical Biometry at Ulm University in Germany, said in a telephone interview. "Our study provides evidence toward giving dietary recommendations in order to prevent asthma and allergies in childhood."